Soundcraftsmen EQ - replacing opamps

[antichef]

I picked up an old Soundcraftsmen "Differential/Comparator Equalizer" Model No. G2241 for pretty cheap - I was hoping to find old-school transformers and inductors inside, but instead found old-school opamps -- I suppose this is a "newer" old unit, and I guess it's no wonder it was cheap (but the general quality of construction seems good to me, I have to say)

Anyway, because of my lingering newbiness there's some novelty for me in merely using an external eq as an optional part of my signal chain - I hooked it into Logic Express using the "I/O" plugin, and it's not bad, but now I'm wondering about the opamps:

It uses 4136CP chips - I guess these are early quad opamps. I'd like to replace them, because I bet I could get more headroom (they seem to distort when the sliders are above the '0' position) and better sound. I read elsewhere that the pinout is different from what's around nowadays, and so I'd probably need to use an adapter of some sort.

Anyone have a suggestion for a replacement and an adapter?

 

[Minion]

The 4136CP is an OLD Quad opamp simular to the 741 ...This opamp is pretty noisy compared to modern opamps and you could probably get some improvement by replaceing them....

Any modern Quad audio opamp would work but I suggest maybe something like the OPA4134 , but because these are quad opamps you might be a bit limited in the selection of opamps because not all opamps come in quads....

You might also want to replace the electro caps in the unit and replace any Tantilum caps with electro"s and any ceramics with Poly.....

Good luck

 

[Somnium7]

You might also want to replace the electro caps in the unit and replace any Tantilum caps with electro"s and any ceramics with Poly.....

This is sound advice. Better quality capacitors and bypassing electrolytic coupling caps with poly can make a significant difference in perceived sound quality.

Also, I recommend rebuilding the power supply. It has been my experience that improving this area has the greatest impact on the sound quality of old analog gear. Most of that old gear usually just has a cheap 78XX and/or 79XX regulator circuit which is the functional equivalent of powering your gear with a white noise generator.

Before swapping those opamps it would be a smart move to install sockets for them if they aren't already in there. With EQ circuits changing the opamp can lead to some squirly behavior if the circuit is designed specifically for the input impedance of a certain opamp. Usually a unit with a higher input impedance is alright but it nice to have the option to try a few different devices out in the actual circuit to see which is the best performer.

Wasn't Mackie the main design guy for Soundcraftsmen stuff?
I thought I read something about that somewhere....

 

[antichef]

Thanks! I definitely want to socket the opamps - they're not already socketed. Don't have it front of me now, but I think the 4136's have inline pins, and it seems they may have what today is a non-standard pin-out (the standards were still in flux for quad opamps when these were new, apparently).

I'll read up on the history some more - I know the company was acquired in 1991 by MTX and the line existed until the mid 1990's (got that off a website) - this may be one of the latter ones.

I'll inventory and replace the caps -- I'll have a look at the power supply, too -- that's starting to get over my head (OK, it is over my head), but I know enough not to get seriously injured On the bright side, the unit isn't noticeably noisy now, unless it's being pushed too hard.

[not proud of this story but... I did some similar work on an ART Tube MP over this last weekend. It came out sounding a little better and looking a lot worse - but only on the inside , so I'm slowly getting the hang of this. After spending a bunch of time on it, I decided to test, and absent-mindedly plugged it in with the 16 volt wall wart used by a Presonus TubPre instead of the 9 volt wall wart that it wants. I briefly stepped in the next room to grab a mic and heard the impact of the metal casing of an electrolytic cap hitting the inside of the metal case - bang! - unplugged it, waved away the smoke, cleaned off the circuit board (that took some time), went to Fry's and got a replacement cap, put it in, and it works fine -- that's a courage builder ]